In the prior art, small aircraft typically include a tail wheel that engages the ground during takeoff and, when the aircraft is landing, re-engages the ground with a “bump” that may be severe. Prior art small aircraft typically include what is supposed to be a shock absorbing system consisting of leaf springs. There are primarily two types of aircraft that employ tail wheel leaf springs. The first is an aircraft having an aluminum outer shell riveted to bulkheads and stringers. The second type has an airframe made of tubular inner structure covered with fabric. The present invention comprises an effective replacement of the tail wheel suspension of either type.
In this regard, reference is made to FIGS. 1 and 2 which show the prior art leaf spring system. An aircraft (FIG. 2) is generally designated by the reference numeral 1 and includes a tail wheel 3 connected to the fuselage 4 by a bracket 6 and a fastener 7 which may consist of one or more bolts fixed with nuts (not shown). Three leaf springs 8 usually constructed of tempered steel engage one another and extend from the fastener 7 through the fastener 6 and curve downward where they are attached by another fastener 9 to a bracket 10 from which emanates a fork 11 to which the wheel 3 is rotatably attached via an axle (not shown) fastened by fasteners 13, one of which is seen in FIG. 2. The bracket 10 also supports the fork 11 for rotation about a vertical axis to allow the wheel 3 to rotate about that axis. The springs 8 are typically 1.25″ to 1.75″ wide. Side loads cause them to twist laterally, causing the tail wheel to shimmy and stressing the springs 8 and their mounts.
If desired, tension springs 15, 17 may be employed to provide a restoring force once the wheel 3 engages the ground and causes flexing of the leaf springs 8.
Other problems arise in the leaf spring suspension systems. In particular, when installed, the leaf springs have a factory pre-set degree of bending. Over time, the leaf springs can change in configuration, flattening out to some degree. This results in lowering of the rear of the fuselage and changing the angulation of the tail wheel 3 with respect to the fuselage and runway. As a result, tail wheel shimmy can result. What is meant by tail wheel shimmy is that the tail wheel can pivot side-to-side as the aircraft is traveling down the runway similar to what one sees in a grocery cart. This shimmying of the tail wheel can adversely impact control of the aircraft while at the same time causing vibrations that can damage the fuselage. In such circumstances, it is necessary to remove the leaf springs and bend them back to original factory specifications. This can be time consuming, labor intensive, and expensive.
Another problem encountered in an aircraft tail wheel is that it is typically pneumatic. In other words, the tail wheel is filled with pressurized air or other gas. When leaf spring suspension systems are used, their stiffness requires a gas-filled tail wheel because the tail wheel acts as a further shock absorber to supplement the limited shock absorbing capability of stiff leaf springs. It would be advantageous if a shock absorbing system for an aircraft tail wheel were provided that provides sufficient flexibility and resiliency in shock absorbing capability that a solid rubber or synthetic rubber tail wheel could be used. Such a configuration would eliminate maintenance and safety problems resulting from flat tires.
While the intention of the prior art suspension illustrated in FIGS. 1 and 2 is to cushion engagement of the wheel 3 with the runway upon landing, in fact, the leaf springs 8 are substantially ineffective in doing so. Rather, they are so stiff that when the wheel 3 engages the runway, little cushioning takes place and forces are transmitted from the wheel 3 to the fuselage 4 causing stresses to the fuselage 4 which can result in structural damage. In fact, typically the tail wheel bounces several times in a bouncing effect, until the bouncing dissipates due to the lack of resiliency of the leaf springs.
Additionally, forces transmitted from the wheel 3 to the fuselage 4 are also felt by the pilot and passengers as a significant bump which can be jarring. Typically, the leaf springs lose their arched configuration over time such that the tail wheel becomes misaligned with respect to the geometry of the aircraft. The only solution is expensive leaf spring replacement. Accordingly, a need has developed for a suspension for the tail wheel of a small aircraft that effectively performs the function of cushioning the effect of the tail wheel engaging the runway during a landing. It is with this need in mind that the present invention was developed.